This invention relates to cardiac rhythm management devices for the heart. In addition, the invention relates to linear stimulation of the heart in order to provide improved hemodynamic benefits.
A normal human heart 100, as illustrated in FIG. 1, includes a right atrium 106, a left atrium 110, a right ventricle 131, and a left ventricle 132. The ventricles 131,132 further comprise a right ventricular free wall 133, a left ventricular free wall 134, and an interventricular septum 135 dividing the ventricles. The electrical propagation system of the heart includes a sinoatrial (SA) node 120, an atrioventricular (AV) node 122, a bundle of His 124 dividing into a right branch of bundle of His 126 and left branch 128, and a plurality of Purkinje fibers 112 dispersed throughout ventricular myocardium 136.
During normal contraction, the SA node 120 initiates the excitation of the heart 100, sending an electrical cardiac pulse through the atria and ventricles. Once initiated by the SA node 120, the cardiac pulse is transmitted through right and left atria 106,110, causing the atria to contract and pump blood from the atria to the ventricles. The cardiac pulse is then further transmitted through the AV node 122 to ventricles 131,132. Transmission in the ventricles 131,132 is accomplished using a conduction system including the bundle of His 124, which divides into the right branch 126 and left branch 128, and finally the Purkinje fibers positioned throughout the ventricular myocardium 136. The transmitted cardiac pulse causes the ventricles to contract, pushing the blood from the ventricles out into the pulmonary and systemic circulatory systems.
In patients with certain heart abnormalities, such as, for example, congestive heart failure and left bundle branch block, the electrical conduction patterns of the left ventricle 132 can be altered or impaired. These abnormalities can in turn cause the interventricular septum 135 to contract before the left ventricular free wall 134, creating asynchronous left ventricular contraction and causing impaired hemodynamic function.
Recently, it has been demonstrated that through the use of atrial synchronous ventricular pacing, the left ventricular contractions in patients with the heart abnormalities described above can be resynchronized. Resynchronization differs from typical pacing performed by devices such as a pacemaker in that the goal of resynchronization is not to alter the rate at which the heart is contracting, but instead to alter the manner in which the contraction occurs. Resynchronization is a process that can involve the application of an electrical stimulus to the left ventricle or both the left and right ventricles after pacing has been detected in the atria. This electrical stimulus forces the septum 135 and free wall 134 to contract at approximately the same time, thereby resynchronizing left ventricular contraction. This resynchronization provides both acute and chronic hemodynamic benefits.
At present, resynchronization has been implemented by resynchronizing the left ventricle or both ventricles using a single point source for each ventricle. An example of a prior art cardiac rhythm management (CRM) device using a single point source is shown in FIG. 2. The left ventricle 132 illustrated in FIG. 2 includes the interventricular septum 135 and interventricular free wall 134 with free wall points 236,237 noted. The resynchronization system 200 includes CRM device 201, lead 203, and single point source 205. The single point source 205 is typically coupled via the lead 203 to the CRM device 201, with the CRM device 201 providing the electrical stimulus for resynchronization. Single point source 205 is constructed with a small surface area such that single point source 205 contacts only a small region of the surface of the left ventricular free wall 134 where point source 205 is located, such as at free wall point 237.
Electrical propagation using a single point source differs from that of the propagation of a cardiac pulse during normal sinus rhythm. In normal sinus rhythm, the bundle of His 124 and Purkinje fibers 112 enhance conduction so that the entire ventricle is activated almost instantaneously, thereby causing the left ventricular contraction time to be very short in duration. In contrast, using a single point source, such as 205 as shown in FIG. 2, electrical propagation from the site at which the single point source contacts the surface of the left ventricle 132 at free wall point 237 to the rest of the ventricular muscle, such as free wall point 236, is much slower, prolonging the left ventricular contraction time. This prolongation of contraction time compared to normal contraction makes the ventricle less efficient.
A further limitation of resynchronization through use of a single point source is the inability to adequately alleviate local wall stress. Local wall stress is a phenomenon that occurs when the interventricular septum 135 contracts before the ventricular free wall 134, forcing the blood contained within ventricle 132 that is displaced by the septum 135 to push against and distend free wall 134. A reduction in local wall stress has been shown through use of a single point source 205, as shown in FIG. 2. However, this reduction in local wall stress is limited to the area immediately adjacent to free wall point 237, and other remote areas of the ventricular free wall, such as free wall region 236, may still exhibit local wall stress.
Therefore, although some advantage may be gained through use of a single point source to assist in resynchronization of the left ventricular free wall and interventricular septum contractions, use of a single point source may still result in a hemodynamically suboptimal situation.
Generally, the present invention relates to cardiac rhythm management devices for the heart. In addition, the invention relates to linear stimulation of the heart in order to provide improved hemodynamic benefits. In one aspect of the disclosure, a method of resynchronization of a heart may comprise the steps of coupling a linear source to a cardiac rhythm management device via a lead, coupling the linear source to a surface of the heart; and resynchronizing a contraction of the heart through linear excitation of the surface by the linear source.
In another aspect, the disclosure provides another method of resynchronization of a heart comprising the steps of coupling a first linear source to a left ventricular free wall nearer an apex of the heart and sending a first electrical stimulus to the first linear source.
In still yet another aspect, the disclosure provides an apparatus to resynchronize a heart by using atrial synchronous ventricular pacing comprising a cardiac rhythm management device, linear source coupled to a portion of a ventricular myocardium surface of the heart, and a lead coupled at a first lead end to the cardiac rhythm management device and at a second lead end to the linear source.
In still yet another aspect, the disclosure further provides an apparatus to resynchronize a heart comprising first means for providing an electrical stimulus to stimulate the heart, second means for exciting a linear region of a surface of the left ventricle, and means for electrically coupling the first means to the second means.
In still yet another aspect, the disclosure provides an apparatus to resynchronize contraction of a left ventricular free wall of a heart using atrial synchronous ventricular pacing, the apparatus comprising a cardiac rhythm management device for creating an electrical stimulus, a lead coupled to the cardiac rhythm management device at a first lead end, and a linear source coupled to the lead at a second lead end. Further in this aspect, the linear source may comprise a contact surface coupled to the left ventricular free wall at a free wall region, wherein the contact surface spans in a linear direction and wherein the contact surface transmits the electrical stimulus so as to linearly excite the free wall region along the entire contact surface and thereby promote resynchronization of contraction of the left ventricular free wall.
The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The figures and the detailed description that follow more particularly exemplify these embodiments.